1. Field of the Invention
The present invention relates to a carbodiimide composition with suppressed yellowing, a stabilizer against hydrolysis mainly comprising the carbodiimide composition and a thermoplastic resin composition containing the same. More specifically, the present invention relates to a carbodiimide composition comprising a carbodiimide compound and an antioxidant, having a 5% weight loss temperature not lower than 250° C. as determined by a thermogravimetric (TG) method, a stabilizer against hydrolysis mainly comprising the carbodiimide composition and a thermoplastic resin composition containing the same.
2. Description of the Prior Art
A carbodiimide compound has a carbodiimide group represented by [—N═C═N—] in a molecule and characteristics such as reactivity with an active hydrogen (for example, hydrogen in carboxylic acids, amines, alcohols and thiols), good adhesion, superior heat resistance and ability to be processed into various forms (such as varnish, powder and film), and is utilized in a variety of applications including crosslinking agents and additives, adhesives, resin modifiers, heat insulating materials, sound absorbing materials and gaskets.
A carbodiimide compound has, however, the problem that the compound itself has is a high yellow index, which means when it is added to plastic materials, it causes the plastic materials to turn yellow or show yellowing by light or heat with passage of time.
In addition, a carbodiimide compound is widely used as a stabilizer against hydrolysis for an ester-group-containing resin or a biodegradable plastic. However, a compound with low molecular weight such as a monocarbodiimide also has problems such as causing an environmental pollution by generating a component having an offensive odor or losing the addition effect thereof by vaporizing, because of a tendency for easy thermal decomposition during processing.
Polycarbodiimide has been used to solve these problems, but use of this compound is difficult for an application where hue is seriously considered (for example, an application to a fiber for clothing) due to the yellowing problem during processing.
The above-described ester-group-containing resins include, for example, a polyethylene terephthalate resin, a polybutylene terephthalate resin, a polyester polyurethane resin, an unsaturated polyester resin, a maleic resin, a alkyd resin, a polycarbonate resin, a polyester carbonate resin, an aliphatic polyester resin, polyether esters, polyesteramides and polycaprolactones.
Further, biodegradable plastics can be roughly classified to aliphatic polyesters having a polyester group in their molecular chains (including those produced by microorganisms), natural polymers such as cellulose, polysaccharides produced by microorganisms, polyvinyl alcohol (PVA) and polyethers such as polyethylene glycol (PEG).
Among them, polylactic acid of an aliphatic polyester as a plastic material derived from plants, and with there being increasing interest on global environment problems such as CO2 reduction, has been extensively studied in fields such as automotive parts, housings for home electric appliances and clothing.
However, the above-described resins having an ester group (ester-group-containing resins) and biodegradable plastics have poor stability against hydrolysis. In particular, biodegradable plastics including aliphatic polyesters have significantly poor stability, which has made it difficult to use these materials in applications with the same levels of functions (such as strength, water resistance, moldability and heat resistance) as those required of conventional plastics.
From these circumstances, several proposals relating to improvement of stability against hydrolysis of ester-group-containing resins or biodegradable plastics have been made. For example, proposals disclosed include one directed to a method for controlling a biodegradation rate of a biodegradable plastic (see, for example, JP-A-11-80522), or another one directed to a method for stabilizing against hydrolysis of an ester-group-containing resin (see, for example, JP-A-296097 and JP No. 3,122,485).
In spite of these proposals, the above problems of a carbodiimide compound have not been sufficiently solved in applications where hue is seriously considered, such as fibers, films and sheets, because of the yellowing of a carbodiimide compound when utilized as a stabilizer against hydrolysis.